Room temperature vulcanizable silicone rubber stocks

ABSTRACT

A ROOM-TEMPERATURE VULCANIZABLE SILICON RUBBER STOCK IS PREPARED BY ADMIXING AN ESSENTIALLY LINEAR DIORGANOPOLYSILOXANE HAVING REACTIVE END GROUPS, PREFERABLY HYDROXYL END GROUPS, AND AS A CROSSLINKER A MIXTURE OF AN AMINOSILANE AND AN OXIME SUBSTITUTED SILANE. THESE MATERIALS CAN BE STORED IN THE ABSENCE OF MOISTURE AND WILL CURE TO FORM ELASTOMERIC PRODUCTS UPON EXPOSURE TO MOISTURE.

United States Patent U.S. Cl. 260-46.5 G 6 Claims ABSTRACT OF THE DISCLOSURE A room-temperature vulcanizable silicone rubber stock is prepared by admixing an essentially linear diorganopolysiloxane having reactive end groups, preferably hydroxyl end groups, and as a crosslinker a mixture of an aminosilane and an oxime substituted silane. These materials can be stored in the absence of moisture and will cure to form elastomeric products upon exposure to moisture.

This application is a continuation-in-part of United States patent application Ser. No. 63,608 filed Aug. 13, 1970 (now US. Pat. No. 3,674,738), said application claimed priority under 35 U.S.C. 119 from German patent application No. P 19 41 285.2 filed Aug. 13, 1969.

This invention relates to a novel room-temperature vulcanizable silicone rubber stock which can be stored in the absence of moisture and cures upon exposure to moisture based particularly on a novel crosslinking organosilicon compound.

Room-temperature vulcanizable silicone rubber stocks are well known in the art as RTV silicone rubbers. These materials have been prepared as two general types or systems; namely, one component stocks wherein all the ingredients are combined in a single package which protects the mixture from moisture and the stock cures upon exposure to moisture; and two component stocks wherein the ingredients are packaged in at least two separate containers and are mixed just prior to use and may not require the presence of moisture for cure. Each system has advantages and the present invention is directed to a new RTV silicone rubber stock which falls into the one component category.

In preparing the one-component RTV silicone rubber stocks, one generally employs a linear diorganopolysiloxane having reactive end groups, a polyfunctional crosslinking organosilicon material and, optionally, a curing catalyst. This invention introduces a novel polyfunctional crosslinking organosilicon material containing both oxime and amino functionality.

It has been known to prepare one-component RTV silicone rubber stocks with linear, hydroxyl endblocked diorganosiloxane polymers and polyfunctional amino substituted silicon compounds or polyfunctional oxime substituted silicon compounds (see, e.g., German patent publication No. 1,120,690, US. Pats. No. 3,453,307 and No. 3,189,576). (For the sake of brevity, those one-component RTV silicone rubber systems cured with amino substituted silicon compounds will be called amino one-component systems and those cured with oxime substituted silicon compounds will be called oxime one-component systems.)

The amino and oxime one-component RTV silicone rubber systems exhibit advantages over other one-component RTV systems. One such advantage is that these systems do not produce corrosive materials, during cure as do the known acetoxy based systems, for example. Also.

offensive odor and slow cure are avoided by the use of the oxime and amino systems.

It is the primary object of this invention to introduce a novel RTV silicone rubber stock. A further object is novel aminooximeorganosilanes and oligomers which are particularly useful as crosslinkers in RTV silicone rubber stocks. Other objects and advantages of this invention are detailed in or will be apparent from the disclosure and claims which follow.

This invention introduces a one-component RTV silicone rubber stock, stable in the absence of moisture, consisting essentially of (A) an essentially linear diorganopolysiloxane having chemically reactive endblocking units, and (B) a crosslinking hydrolyzable silicon compound selected from silanes and their oligomers containing in each molecule an average of at least 0.5 oxime groups bonded to silicon through oxygen atoms and at least 0.5 amine groups bonded to silicon through Si-N linkage, each molecule containing a total of at least 3 oxime and amino groups, any remaining silicon valences being satisfied by monovalent hydrocarbon or substituted hydrocarbon atoms or by oxygen atoms present as siloxane linkages.

The essentially linear diorganopolysiloxanes (A) are well known in the art and are available commercially. The best known and most widely employed of this polymer has hydroxyl endblockers and can be defined by the general formula where R is a hydrocarbyl or substituted hydrocarbyl radical, x has an average value of 0.99 to 1.01, y has an average value of 1.99 to 2.01, x-i-y is 3.0'and n has a value of at least 3 but more preferably at least 50 and can have a value such that the polymer is gum-like and has a viscosity exceeding 1,000,000 cs. at 25 C. The hydroxyl groups in the above formula can be replaced, totally or partially, with other reactive end groups such as RHN-, oxime groups, silicon bonded hydrogen atoms, alkoxy groups or alkoxyalkoxy groups. The polymers are generally made up of R SiO units but small amounts, preferably below 2 mol percent, of RSiOs a R SiO and even SiO units can be tolerated. The more nearly the value of y approaches 2.00, the better the ultimate product. The operable polymers are well known and fully described in the prior art as in U.S. Pats. No. 3,127,363, No. 3,082,526, No. 2,927,907, No. 2,843,555 and No. 3,184,427.

The organic substituents represented by R include hydrocarbyl radicals such as alkyl radicals such as methyl, ethyl, isopropyl and octadecyl radicals; alkenyl radicals such as vinyl, allyl and octadecenyl radicals; cycloaliphatic radicals such as cyclopentyl, cyclohexyl, cyclohexenyl and methylcyclohexyl radicals; aryl radicals such as phenyl, xenyl and naphthyl radicals; aralkyl radicals such as benzyl, beta-phenylethyl and beta-phenylpropyl radicals; and alkaryl radicals such as tolyl radicals, propylphenyl radicals and ethylphenyl radicals. R can also be a substituted hydrocarbyl radical such as a halogeno hydrocarbyl radical including chloro, fluoro, 'bromo and iodo substituted derivatives of the above defined and exemplified hydrocarbyl radicals and particularly chlorophenyl, perfluoroalkylethyl such as CF CH CH per chlorovinyl and chloromethyl as well as cyanoalkyl radicals such as beta-cyanoethyl. It is preferred that at least 50 percent of the R groups be methyl radicals and the remaining R groups, if any, phenyl, vinyl or both.

The R groups on any one silicon atom can be the same or different. The polymers can be homopolymers, copolymers. mixtures of homopolymers or copolymers or both and the degree of polymerization can be over a narrow or wide range. Preferably, the diorganopolysiloxane has a viscosity in the range from 100 to 500,000 cs. at 25 C.

The second ingredient herein is the crosslinking agents (B) which are novel silanes or oligomers of such silanes. The crosslinking agent (B) must contain an average of at least 0.5 oxime groups bonded to silicon through an oxygen atom and an average of at least 0.5 amino groups bonded to silicon through an Si-N linkage and a total of at least 3 of such oxime and amino groups per molecule. The remaining valences of the silicon atoms in such silanes and oligomers can be satisfied by hydrocarbyl or substituted hydrocarbyl radicals as defined for the symbol R and by oxygen atoms present as siloxane linkages (SiOSi). The preferred silane crosslinking agents (B) are defined by the general formula where R is as above defined, R is hydrogen or a radical as defined for R, X is where R is as above defined and R is a hydrogen or a hydrocarbyl or substituted hydrocarbyl radical free of aliphatic unsaturation, and R is a divalent hydrocarbon or halogenohydrocarbon radical, a is or 1, b and c each have an average value of at least 0.5, the sum of b and c is 3 or 4 and a+b+c is 4. Preferably, R is hydrogen, the R radical in the amino group is n-butyl or cyclohexyl. Examples of the divalent R group include hydrocarbon radicals and substituted hydrocarbon radicals which form a ring with the carbon atom of the and -CH CH (CH{CCl CH The su bstit-uent group ON=X is fully described and exemplified in U.S. Pats. No. 3,184,427 and No. 3,189,576, incorporated herein by reference.

As can be seen from the required average value of at least 0.5 for b and c, mixtures of various silanes of the above formulae can be employed. Furthermore, oligomers of the defined silanes and mixtures of such silanes and their oligomers, for instance, as they appear upon preparation of such silanes, can be used.

Furthermore, in place of the defined novel silanes which display both amino and oxime groups in each molecule, mixtures of silanes containing only oxime groups with silanes containing only amino groups and oligomers of such silanes can be used. Examples of silanes containing only oxime groups as the hydrolyzable group containing nitrogen are particularly defined by the general formula R Si(ON=X) where R, X and a are as above defined. Examples of silanes containing only amino groups as the hydrolyzable group containing nitrogen are particularly defined by the general formula where R, R and a are as above defined. Preferably, in both types of silanes a has a value of 1.0. However, it

is required that the mixture of silanes have an average of at least 0.5 oxime groups and 0.5 amino groups per silicon atom present and a total average of at least 3 oxime and amino groups per molecule in the mixture. The oligomers of such silanes are prepared by known methods involving partial hydrolysis and condensation of the silanes to produce low molecular weight siloxanes of 2 to 10 silicon atoms, e.g. (X=NO) RSiOSi(ON=X) R and The silanes of the formulae set out above and employed as crosslinking agents herein can be prepared by reacting a halogenosilane with an oxime of the formula X=NOH, where X is as above defined, a primary or secondary amine of the formula RRNH, wherein R and R are as above defined, or mixtures of such oximes and amines. Preferably, the reaction is carried forward in the presence of an acid acceptor such as triethylamine, pyridine or alpha-picoline or a mixture thereof. The reaction is carried forward at room temperature, preferably in an inert solvent such as toluene and under exclusion of water. In short, the procedures and reactions employed to prepare the oxime-aminosilanes employed herein are those known for the reaction of halogenosilanes with oximes and amines individually. The defined crosslinking agent (B) is employed in proportions such that there is a total of at least 1 mol of the crosslinking agent (B) per gram equivalent of reactive end groups in the diorganopolysiloxane (A). In practice, 0.2 to 15 percent by weight of crosslinker (B), preferably 1 to 10 percent by weight, is present in the mixture of diorganopolysiloxane (A) and crosslinking agent (B). Operable condensation catalysts include those catalysts disclosed in U.S. Pats. No. 3,127,363, No. 2,843,555 and No. 2,927,907, among others.

In addition to the diorganopolysiloxane (A) and de fined crosslinking agent (B), the RTV silicone rubber stocks of this invention can contain fillers and other additives well known for use in such stocks and employed in their standard or known proportions. Such additional materials include reinforcing fillers, non-reinforcing fillers, pigments, soluble dyes, silicone resins, organic resins such as polyvinylchloride powder, corrosion inhibitors, perfumes and other aromatics, oxidation inhibitors, heat stabilizers, solvents, condensation catalysts such as dibutyltindilaurate, dibutyltin di 2 ethylhexoate and organosiloxytitanium compounds as well as organic titanates, and softeners and plasticizers such as diorganosiloxanes having nonreactive endblockers such as trimethylsiloxy endblocked dimethylpolysiloxanes. If some of the organosilicon compounds and polymers present in the RTV silicone rubber stocks of this invention are aliphatically unsaturated organic substituents such as vinyl, allyl and cyclohexenyl radicals, it is desirable to include 0.01 to 5 percent by weight of an organic peroxide based on the weight of the diorganopolysiloxane present.

It is generally the practice to employ fillers in silicone rubber stocks and operable fillers herein include reinforcing fillers which typically have a surface area of more than SO'square meters per gram and include fume silicas, silica aerogels, precipitated silicas and other high surface area fillers; non-reinforcing fillers having surface areas below 50 square meters per gram and exemplified by quartz flour, diatomaceous earth, calcium silicate, zirconium silicate, the so-called moleculer sieves, calcium carbonate and certain carbon blacks. Also operable are fibrous fillers such as asbestos, glass fibers and organic fibers. The fillers can be pre-treated to display organosiloxy or alkoxy groups on their surface. Mixtures of fillers can be used. In general, the fillers are employed in standard proportions well known in the art with excellent results achieved with 5 to percent filler based on the total weight of organopolysiloxane (A) and filler.

The RTV silicone rubber stocks of this invention can be prepared by any desired means for mixing such stocks but water sould be excluded from the ingredients prior to mixing and the mixing should be carried forward in the absence of water vapor.

The RTV silicone rubber stocks of this invention are packaged and stored in the absence of and under exclusion of water in any form. The stocks cure to form elastomeric products at room temperature when exposed to moisture. In general, the moisture present in the atmosphere is sufiicient to bring about the desired vulcanization and cure but in areas where water vapor levels in the atmosphere are very low (i.e. very low humidity) or when a more rapid cure is desired, water or water vapor may be introduced by any desired means. Furthermore,

the cure rate can be advanced, if desired, by increasing the temperature at which the cure is carried forward.

It should be noted that in contrast to the known aminosilane crosslinking agents, the present system has the advantage that they will cure at temperatures below 5 C. and at relative humidity exceeding 60 percent to produce an elastomer whose surface is smooth and shows no undesired wrinkling or crimping. Further, the systems of this invention are superior to the known oximesilane crosslinking systems in that they adhere better to substrates.

The RTV silicone rubber stocks can be vulcanized and cured in thin film or deep section on a wide variety of substrates and will exhibit excellent adhesion to such substrates even in the absence of primers, although it should be understood such primers can be used if desired and may enhance adhesion. Typical substrates to which such adhesion has been noted include glass, porcelain, stone, concrete, mortar, aluminum, stainless steel, copper, wood, paper, polyvinylchloride, coatings of synthetic resin lacquers, various organic plastic surfaces (both thermoplastics and thermoset plastics), and a wide variety of construction materials. The RTV silicone rubber stocks of this invention are useful in all the wide variety of uses presently known for such stocks including preparation of molds, sealing joints and hollow areas, as adhesives, for putty masses for preparing protective coatings, paper coatings to achieve release or abhesive surfaces, insulation on electrical conductors, as shatter-resistant coatings on glassware and other frangible materials, especially light bulbs, and in preparation of intricate and delicate molds for waxes and similar materials.

The following examples are included herein to assist those skilled in the art to gain a full understanding of the invention. The examples are not intended to define or limit the scope of the invention and the various equivalent materials noted above in this disclosure can be substituted in chemically equivalent amounts in any of the examples with equivalent results being achieved and realized. All parts and percentages are based on weight and all viscosities were measured at 25 C.

The crosslinking agent (B) employed in Examples 1 and 2 was prepared as follows. A solution of 174 grams of methylethylketoxime in 800 ml. of toluene was added dropw se at room temperature, under exclusion of moisture, with concurrent stirring to a solution of 149.5 grams of CH S1Cl and 336 grams triethylamine in 2.3 liters of toluene. After the addition was completed, the reaction mixture was stirred for two hours at room temperature. Then a solution of 115 grams of cyclohexylamine in 400 ml. of toluene was added to the mixture dropwise, with concurrent stirring at room' temperature and with the careful exclusion of moisture from the reaction zone After the addition of the cyclohexylamine solution was completed, the reaction mixture was stirred for an additional three hours at room temperature. The reaction mixture was filtered to remove precipitate and the precipitate was washed with toluene. The toluene which was used to wash the precipitate was combined with the filtrate and e solution thus obtained was stripped by heatin at 140 C. at atmospheric pressure and then at 70 C. at 10 mm. Hg (abs.) pressure. The residue was filtered and 286 g. of filtrate was obtained. The fluid filtrate was analyzed by elemental analysis as Well as recognized analytical techniques and proved to be essentially the silane of the formula (a) grams of a mixture of 50 parts hydroxyl endblocked dimethylpolysiloxane having a viscosity of 50,000 cp./25 C., 20 parts calcium silicate filler and 10 parts fume silica was mixed with 5 grams of the fluid prepared above employed as the crosslinking silane and 0.1 g. dibutyltindilaurate. This mixture was mass A.

(b) For purposes of comparison, the procedure described in (a) above was repeated but the crosslinking agent employed was 5 g. of

This mixture was mass B.

The mixtures so prepared (Mass A and Mass B) were stored with moisture excluded and showed no deterioration after several months storage. The masses A and B vulcanized and cured to form elastomers when exposed to atmospheric moisture at room temperature.

The masses A and B were compared as to adhesion to concrete employing tear machines according to the standards set down in Guides for Testing Joint Materials in Prefabricated Concrete Construction (issued June 1967), reprinted in Beton and Stahlbau, vol. 62, 1967, No. 9, reprint 2.4.1 and according to test articles stored in accordance with reprint 2.4.2 and adhesive strength of elastomers prepared on other substrates of elastomers prepared on other substrates according to the American Standards Association Method 116.1. The following results were obtained.

Adhesive strength in kgJsq. cm.

Cured Stainless polyvinylste Substrate chloride Aluminum (V m) Concrete Mass A 3. 5 10. 1 2. 5 3. 0 Mass B 0 1. 8 0. 8 1. 8

EXAMPLE 2 (c) A mixture weighing 100 grams was prepared from 32 parts a,w-dihydroxydimethylpolysiloxane having a viscosity of 80,000 cp./25 C., 15 parts a,w-trimethylsiloxydimethylpolysiloxane having a viscosity of 33 cp./25 C., 45 parts quartz flour and 8 parts fume silica. The foregoing mixture was further mixed with 4.5 grams of the silane EXAMPLE 3 The procedure in Example 1(a) was repeated except the crosslinking silane employed was 5 grams of a mixture of 2 mols of CH Si{ON=C(CH (C H and 1 mol of methyltris(cyclohexylamino)silane. The mixture so ob tained could be stored in the absence of moisture and upon exposure to atmospheric moisture it cured to form an elastomeric product. The adhesion of this RTV silicone rubber stock was tested as inExample 1 above with the following results:

ADHESIVE STRENGTH IN KG./SQ. CM.

Substrate:

Cured polyvinylchloride 3.3 Aluminum 10.4 Stainless steel (V A) 2.8 Concrete 3.1

EXAMPLE 4 Equivalent results were achieved when Example 1(a) was repeated with 5 g. of each of the following silanes or their oligomers:

[( 1116)( 1) ls lNCI-I1( 1 11)]b where a is 1 or 2, b is 1 or 2 and a+b is 3.

EXAMPLE Equivalent results are achieved when Example 4 is repeated employing as the base siloxane polymer any of the following:

CH3 HO S1O 11 6115 HOKOHahSiOlssl(CuHOzSiOhH That which is claimed is:

1. A room-temperature vulcanizable silicone rubber stock which is inert in the absence of moisture and cures on exposure to moisture consisting essentially of a mixture of (A) an essentially linear diorganopolysiloxane having chemically reactive endblocking groups selected from the group consisting of --OH, -NHR, oxime radicals, H, alkoxy radicals and alkoxyalkoxy radicals where R is a hydrocarbyl or halogenohydrocarbyl radical of 1 to 18 carbon atoms or a cyanoalkyl radical, the organic substituents on said linear diorganopolysiloxane being hydrocarbyl radicals or halogenohydrocarbyl radicals of l to 18 carbon atoms or cyanoalkyl radicals, and (B) 0.2 to 15 percent by weight based on the total weight of (A) and (B) of a crosslinking agent which is a mixture of silanes of the formulae R,,Si(ON=-=X) and wherein R is as above defined, R is a hydrogen atom or R radical, X is a radical of the formula where R is as above defined, R is a hydrogen atom or an R radical, R is a divalent hydrocarbon or halogenated hydrocarbon radical .and a is 0 or 1, said mixture containing an average of at least 0.5 -ON=X groups and 0.5 --NRR' groups per silicon atom present and a total average of at least 3 ON=X and --NRR' groups per molecule in the mixture.

2. A room-temperature vulcanizable silicone rubber stock, stable in the absence of moisture and curable in the presence of moisture to form elastomers consisting essentially of (A) an essentially linear, hydroxyl endblocked diorganopolysiloxane of the general formula wherein R is a hydrocarbyl radical of 1 to 18 carbon atoms, a halogenohydrocarbyl radical of 1 to 18 carbon atoms or a cyanoalkyl radical, x has an average value of 0.99 to 1.01, y has an average value of 1.99 to 2.01, and n has a value such that the viscosity of the polymer is in the range from to 500,000 cs. at 25 C., and (B) 0.2 to 15 percent by weight :based on the total weight of (A) and (B) of a mixture of silanes and oligomers of such silanes of the general formulae R Si(ON=X) and R,,Si(NRR) wherein R is as above defined, R is a hydrogen atom or an R radical, X is a radical of the formula where R is as above defined, R is hydrogen or a R radical, R is a divalent hydrocarbon or halogenated hydrocarbon radical, a is 0 or 1, there being present in the crosslinking agent (B) an average of at least 0.5 -ON=X and 0.5 -NRR groups per silicon atom.

3. The silicone rubber stock of claim 2 also containing a filler.

4. The silicone rubber stock of claim 2 also containing a condensation catalyst.

5. The silicone rubber stock of claim 2 also containing a filler and a condensation catalyst.

6. The silicon rubber stock of claim 1 also containing a filler and a condensation catalyst.

References Cited UNITED STATES PATENTS 3,189,576 6/1965 Sweet 26046.5 3,464,951 9/1969 Hittmair et a1 26037 3,674,738 7/1972 Nitzsche et al. 26046.5 G

M. I. MARQUIS, Assistant Examiner DONALD E. CZAJA, Primary Examiner U.S. Cl. X.R.

117-423 D, 124 F, 135.1, 138.8 R, 148; 26018 S, 37 SB, 46.5 E, 825, 827

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENTNU. 2 3,758,441. DATED September 11, 1973 INVENTUR(S) Siegfried Nitzsche, et al It is certified that errorappears in the above-identified patentand thatsaid Letters Patentis hereby corrected asshown below:

In column 6, lines 12, 50, and 52, "cp./25" should read Signed and Scaled this Twelfth Day of March 1985 [SEAL] Attest:

DONALD J. QUIGG Attesting Officer Acting Commissioner of Parents and Trademarks 

